1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus suitably used for small-size apparatuses having an imaging function, particularly, digital still cameras, camera phones, personal digital assistances (PDAs), and the like.
2. Description of Related Art
In recent years, imaging apparatuses such as digital still cameras have been required to be smaller in overall size as imaging devices such as charge coupled devices (CCDs) and complementary metal oxide semiconductors (CMOS's) have become smaller. Therefore, recently, a zoom lens has been developed in which the size in the direction of the thickness when the lens is incorporated in an imaging apparatus is reduced by bending the optical path of the lens system in the middle to form a so-called bending-type optical system.
As a zoom lens using the bending-type optical system, JP-A-2003-202500 discloses examples of a four-group zooming system including in order from the object side: a first lens group having a positive refractive power and including a reflecting member that bends the optical path; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a positive refractive power. In this system, the power-varying is performed by moving the negative second lens group and the positive fourth lens group. In particular, in the example shown in FIG. 1 of JP-A-2003-202500, two lenses are disposed behind the reflecting member in the first lens group, three lenses are used in the second lens group, and a cemented lens is used in the third lens group.
Since the thickness in the direction of the depth when the lens is incorporated in an imaging apparatus can be reduced by using the bending-type optical system as described above, in recent years, this type of zoom lens has started to be mounted in various imaging apparatuses. On the other hand, there is a demand for cost reduction on the market as well as a demand for size reduction. For this reason, it has been desired that a bending-type optical system being advantageous in cost while being reduced in thickness be developed. For cost reduction, it is considered to use a resin material as the lens material; however, when a resin lens is used whose characteristic change due to the temperature is large compared with that of a glass lens, it is desirable to adopt a structure where sufficient consideration is given to the temperature characteristic. Moreover, in order to reduce the overall size of the lens structure and the cost, it is preferable that the number of lenses is small. The four-group zoom lens described in JP-A-2003-202500 has room for improvement with respect to size reduction and cost reduction.